descent with modification; the idea that living species are descendants of ancestral species that were different from the present-day ones; also defined more narrowly as the change in the genetic composition of a population from generation to generation

Biology

the scientific study of life

Emergent Properties

new properties that arise with each step upward in the hierarchy of life, owing to the arrangement and interactions of parts as complexity increases

The Biosphere

the entire portion of Earth inhabited by life; the sum of all the planet's ecosytems

Ecosystems

all the organisms in a given area as well as the abiotic factors with which they interact; one or more communities and the physical environment around them

Communities

all the organisms that inhabit a particular area; an assemblage of populations of different species living close enough together for potential interaction

Populations

a localized group of individuals of the same species that can interbreed, producing fertile offspring

Organ Systems

a group of organs that work together in performing vital body functions

Organs

a specialized center of body function composed of several different types of tissues

Tissues

an integrated group of cells with a common function, structure, or both

Cells

Organelles

any of several membrane-enclosed structures with specialized functions, suspended in the cytosol of eukaryotic cells

Molecules

two or more atoms held together by covalent bonds

Systems Biology

an approach to studying biology that aims to model the dynamic behavior of whole biological systems

Eukaryotic Cell

a type of cell with a membrane-enclosed nucleus and mebrane-enclosed organelles

organisms with eukaryotic cells (protists, plants, fungi, and animals) are called eukaryotes

Prokaryotic Cell

a type of cell lacking a membrane-enclosed nucleus and mebrane-enclosed organelles

organsims with prokaryotic cells (bacteria and archaea) are called prokaryotes

DNA

a double-stranded , helical nucleic acid molecule, consisting of nucleotide monomers with a deoxyribose sugar and the nitrogenous bases adenine (A), cytosine (C), guanine (G), and thymine (T); capable of being replicated and determining the inherited structure of a cell's proteins

Genes

a discrete unit of hereditary information consisting of a specific nucleotide sequence in DNA (orRNA, in some viruses)

Genome

the genetic material of an organism or virus; the complete complement of an organism's or virus's genes along with its noncoding nucleic acid sequences

Bioinformatics

the use of computers, software, and mathematical models to process and integrate biological information from large data sets

Negative Feedback

a primary mechanism of homeostasis, whereby a change in a physiological variable triggers a response that counteracts the initial change

Positive Feedback

a physiological control mechanism in which a change in a variable triggers mechanisms that amplify the change

Domain Bacteria

Domain Archaea

Domain Eukarya

Inquiry

the search for information and explanation, often focused by specific questions

Discovery Science

the process of scientific inquiry that focuses on describing nature

Data

record observations

Inductive Reasoning

a type of logic in which generalizations are based on a large number of specific observations

Hypothesis

a tentative answer to a well-framed question, narrower in scope than a theory and subject to testing

Deductive Reasoning

a type of logic in which specific results are predicted from a general premise

Controlled Expirement

an expirement in which an experimental group is compared with a control group that varies only in the factor being tested

Theory

an explanation that is broad in scope, generates new hypothesism and is supported by a large body of evidence

Models

a representation of theory or process

Technology

the application of scientific knowledge for a specific purpose, often involving industry or commerce but also including uses in basic research

Compound

a substance consisting of two or more different elements combined in a fixed ratio

Element

any substance that cannot be broken down to any other substance by chemical reactions

Trace Elements

an element indispensible for life but required in extremely minute amounts

Atom

the smallest unit of matter that retains the properties of an element

Neutrons

a subatomic particle having no electrical charge (electrically neutral), with a mass of about 1.7 x 10-24g, found in the nucleus of an atom

Protons

a subatomic particle with a single positive electrical charge, with a mass of about 1.7 x 10-24 g, found in the nucleeus of an atom

Atomic Nucleus

an atom's dense central core, containing protons and neutrons

Dalton

a measure of mass for atoms and subatomic particles; the same as the atomic mass unit, or amu

Atomic Number

the number of protons in the nucleus of an atom, unique for each element and designed by a subscript to the left of the elemental symbol

Atomic Mass

the total mass of an atom, which is the mass in grams of 1 mole of the atom

Isotopes

one of several atomic forms of an element, each with the same number of protons but a differen number of neutrons, thus differing in atomic mass

Radioactive Isotope

an isotope (an atomic form of a chemical element) that is unstable; the nucleus decays spontaneously, giving off detectable particles and energy

Energy

the capacity to cause change, especially to do work (to move matter against an opposing force)

Potential Energy

the energy that ,atter posesses as a result of its location or spatial arrangement (structure)

Electron Shells

an energy level of electrons at a characteristic average distance from the nucleus of an atom

Valence Electrons

an electron in the outermost electron shell

Valence Shell

the outermost energy shell of an atom, containing the valence electrons involved in the chemical reactions of that atom

Orbital

the three-dimensional space where an electron is found 90% of the time

Chemical Bonds

an attraction between two atoms resulting from a sharing of outer-shell electrons or the presence of opposite charges on the atoms

the bonded atoms gain complete outer electron shells

Covalent Bond

a type of strong chemical bond in which two atoms share one or more pairs of valence electron

Molecule

two or more atoms held together by covalent bonds

Single Bond

a single covalent bond; the sharing of a pair of valence electrons by two atoms

Structural Formula

a type of molecular notaion in which the constituent atoms are joined by lines representing covalent bonds

Molecular Formula

a type of molecular notaion representing the quanity of constituent atoms, but not the nature of the bonds that join them

Double Bond

a double covalent bond; the sharing of two pairs of valence electrons by two atoms

Valence

the bonding capacity of a given atoml usually equals the number of unpaired electrons required to complete the atom's outermost (valence) shell

Electronegativity

the attraction of a given atom for the electrons of a covalent bond

Nonpolar Covalent Bond

a type of covalent bond in which electrons are shared equally between two atoms of similiar electronegativity

Polar Covalent Bond

a covalent bond betweena toms that differ in electronegativity

the shared electrons are pulled closer to the more elctronegative and the other atoms lightly positive

Ion

atom or group of atoms that has gained or lost one or more electrons, thus acquiring a change

Cation

a postively charged ion

Anion

a negatively charged ion

Ionic Bond

a chemical bond resulting from the attraction between oppositely charged ions

Ionic Compounds

a compound resulting from the formation of an ionic bond; also called a salt

Salts

a compound resulting from the formation of an ionic bond; also called an ionic compound

Hydrogen Bond

a type of weak chemical bond that is formed when the slightly positive hydrogen atom of a polar covalent bond in one molecule is attracted to the slightly negative atom of a polar covalent bond in another molecule

Van der Waals Interactions

weak interactions between molecules or parts of molecules that result from localized charge fluctuations

Reactants

a staring material in a chemical reaction

Products

a material resulting from a chemical reaction

Chemical Equilibrium

in a chemical reaction, the state in which the rate of the forward reaction equals the rate of the reverse reaction, so that the relative conentration of the reactants and products do not change with time

Polar Molecule

a molecule (such as water) with opposite charges on different ends of the molecule

Cohesion

the binding together of like molecules, often hydrogen bonds

Adhesion

the attraction between different kinds of molecules

Surface Tension

a measure of how difficult it is to stretch or break the surface of a liquid,

water has a high surface tension because of the hydrogen bonding of surface molecules

Kinetic Energy

the energy associated with the relative motion of objects

moving matter can perfom work by imparting motion to the other matter

Heat

the total amount of kinetic energy due to the random motion of atoms or molecules in a body of matter; also called thermal eneergy

heat is energy in its most random form

Temperature

a measure of the intensity of heat in degrees, reflecting the average kinetic energy of the molecules

Celsius Scale

a temperature scale (C) equal to 5/9 (F-32) that measures the freezing point of water at OC and the boiling point of water at 100C

Calorie (cal)

the amount of heat energy required to raise the temperature of 1 g of water by 1C; also the amount of heat energythat 1 g of water releases when it cools by 1C

the Calorie (with capital C), usually used to indicate the energy content of food, is a kilocalorie

Kilocalorie (kcal)

a thousand calories; the amount of heat energy required to raise the temperature of 1kg of water by 1C

Joule (J)

a unit of energy: 1 J =0.2239 cal; 1 cal = 4.184 J

Specific Heat

the amount of heat that must be absorbed or lost for 1 g of a substance to change its temperature by 1C

Heat of Vaporization

the quanity of heat a liqid must absorb for 1 g of it to be converted from the liquid to the gaseseous state

Evaporative Cooling

the process in which the surface of an object becomes cooler during evaporation, owing to a change of the molecules with the greatest kinetic energy from the liquid to the gaseous state

Solution

a lquid that is a homogeneous mixture of two or more substances

Solvent

the dissolving agent of a solution

water is the most versatile solvent known

Solute

a substance that is dissolved in a solution

Aqueous Solution

a solution in which water is the solvent

Hydration Shell

the sphere of water molecules around a dissolved ion

Hydrophilic

having an affinity for water

Colloid

a mixture made up of a liquid and particles that (because if their large size) remain suspended rather than dissolved in that liquid

Hydrophobic

having an aversion to water; tending to coalesce and form droplets in water

Molecular Mass

the sum of the masses of all the atoms in a molecule; sometimes called molecular weight

Mole (mol)

the number of grams of a substance that equals its molecular weight in daltons and contains Avogados's number of molecules

Molarity

a common measure of solute concentration, reffering to the number of moles of solute per litter of solution

Hydrogen Ion

a single proton with a charge of 1+

the dissociation of a water molecule (H20) leads to the generation of a hydroxide ion (OH-) and a hydrogen ion (H+)

Hydroxide Ion

a water molecule that has lost a proton; OH-

Hydronium Ion

a water molecule that has an extra proton bound to it; H3O+

Acid

a substance that increases the hydrogen ion concentration of a solution

Base

a substance that reduces the hydrogen ion concentration of a solution

pH

a measure of hydrogen ion concentration equal to -log[H+] and ranging in value from 0 to 14

Buffers

a substance that consists of acid and base forms in a solution and that minimizes changes in pH when extraneous acids or bases are added to the solution

Organic Chemistry

the study of carbon compounds (organic compounds)

Hydrocarbons

an organic molecule consisting only of carbon and hydrogen

Isomers

one of several compounds with the same molecular formula but different structures and therefore different properties

the three types of isomers are structural isomers, geometric isomers, and enantiomers

Structural Isomers

one of several compounds that have the same molecular formula but differ in the covalent arrangements of their atoms

Geometric Isomers

one of several compounds that have the same molecular formula and covalent arrangements but differ in the spatial arrangements of their atoms owing to the inflexibility of double bonds

Enantiomers

one of two compounds that are mirror images of each other

Functional Groups

a specific configuration of atoms commonly attached to the carbon skeletons of organix molecules and usually involved in chemical reactions

Hydroxyl Group

a chemical group consisting of an oxygen atom joined to a hydrogen atom

molecules possessing this group are soluble in water and are called alcohols

Carbonyl

a chemical group present in aldehydes and ketones and consisting of a carbon atom double-bonded to an oxygen atom

Carboxyl

a chemical group presennt in organic acids and consisting of a single carbon atom double-bonded to an oxygen atom and also bonded to a hydroxyl group

Amino

an organic molecule possessing both carboxyl and amino groups

amino acids serve as the monomers of polypeptides

Sulfhydryl

a chemical group consisting of a sulfur atom bonded to a hydrogen atom

Phosphate

a chemical group consisting of a phosphorus atom bonded to four oxygen atoms; important in energy transfer

Methyl

a chemical group consisting of a carbon bonded to three hydrogen atoms

the methyl group may be attached to a carbon or to a different atom

Adenosine Triphosphate

ATP

an adenine-containing nucleoside triphosphate that releases free energy when its phosphate bonds are hydrolyzed

this energy is used to drive energonic reactions in cells

Macromolecules

a giant molecule formed by the joining of smaller molecules, usually by a condensation reaction

polysaccharides, proteins, and nucleic acids are macromolecules

Polymer

a long molecule consisting of many similar or identical monomers linked together

Monomers

the subunit that serves as the building block of a polymer

Carbohydrates

a sugar (monosaccharide) or one of its dimers (disaccharides) or polymers (polysaccharides)

Lipids

one of a group of compounds, including fats, phospholipids, and steroids, that mix poorly if at all, with water

Proteins

a functional biological molecule consisting of one or more polypeptides folded and coiled into a specific three-dimensional structure

Nucleic Acids

a polymer (ppolynucleotide) consisting of many nucleotide monomers; serves as blueprint for proteins and, through the actions of proteins, for all cellular activities

the two types are DNA and RNA

Condesation Reaction

a reaction in which two molecules become covalently bonded to each other through the loss of a small molecule, usually water, in which case it is also called a dehydration reaction

Dehyrdration Reaction

a chemical reaction in which two molecules covalently bond to each other with the removal of a water molecule

Enzymes

a macromolecule serving as a catalyst, a chemical agent that changes the rate of a reaction without being consumed by the reaction

Hydrolysis

a chemical process that lyses, or splits, molecules by the addition of water, functioning in disassembly of polymers to monomers

Monosaccharides

the simplestcarbohydrate, active alone or serving as a monomer for disaccharides and polysaccharides

also known as simple sugars, monosaccharides have molecular formulas that are generally some multiple of CH20

Disaccharide

a double sugar, consisting of two monosaccharides joined by a glycosidic linkage formed during dehydration synthesis

Glycosidic Linkage

a covalent bond formed between two monosaccharides by a dehydration reaction

Polysaccharides

a polymer of many monosaccharides, formed by dehydration reactions

Starch

a storage polysaccharide in plants, consisting entirely of glucose monokmers joined by alpha glycosidic linkages

Glycogen

an extensively branched glucose storage polysaccharide found in the liver and muscle of animals; the animal equivalent of starch

Cellulose

a structural polysaccharide of plant cell walls, consisting of glucose monomers joined by beta glycosidic linkages

Lipids

one of a group of compounds, including fats, phospolipids, and steroids, that mix poorly, if at all, with water

Fat

a lipid consisting of three fatty acids linked to one glycerol molecule; also called a triclyglycerol or triglyceride

Fatty Acid

a long carbon chain carboxylic acid

fatty acids vary in length and in the number and location of double bonds; three fatty acids linked to a glycerol molecule form a fat molecule, also known as a triglycerol or triglyceride

Triacylglycerol

three fatty acids linked to one glycerol molecule; also called a fat or a triglyceride

Saturated Fatty Acid

a fatty acid in which all carbons in the hydrocarbon tail are connected by single bonds, thus maximizing the number of hydrogen atoms that are attached to the carbon skeleton

Unsaturated Fatty Acid

a fatty acid possesing one or more double bons between the carbons in the hydrocarbon tail

such bonding reduces the number of hydrogen atoms attached to the carbon skeleton

Trans Fats

an unsaturated fat containing one or more trans double bonds

Phospholipids

a lipid made up of glycerol joined to two fatty acids and a phosphate group

the hydrocarbon chains of the fatty acids act as nonpolar, hydrophobic tails, while the rest of the molecule acts as a polar, hydrophilic head

phospholipids form bilayers that function as biological membranes

Cholestrol

a steroid that forms an essential component of animal cell membranes and acts as a precursor molecule for the synthesis of other biologically important steroids, such as hormones

Steroids

a type of lipid characterized by a carbon skeleton consisting of four rings with various chemical groups attached

Enzymes

a macromolecule serving as a catalyst, a chemical agent that changes the rate of a reaction without being consumed by the reaction

Catalysts

a chemical agent that increases the rate of a reaction without being used or consumer by the reaction

Transport Proteins

a transmembrane protein that helps a certain substance or class of closely related substances to cross the membrane

Motor Proteins

a protein that interacts with cytoskeletal elements and other cell components, producing movement of the whole cell or parts of the cell

Polypeptides

a polymer (chain) or many amino acids linked together by peptide bonds

Peptide Bond

the covalent bond between the carboxyl group on one amino acid and the amino group on another; formed by a dehydration reaction

Primary Structure

the level of protein structure referring to a specific sequence of amino acids

Secondary Structure

the localized, repetitive coiling or folding of the polypeptide backbone of a protein due to hydrogen bond formation between constituents of the backbone

Tertiary Structure

irregular contortions of a protein molecule due to interactions of side chains involved in hydrophobic interactions, ionic bonds, hydrogen bonds, and disulfide bridges

Hydrophobic Interaction

a type of weak chemical bond formed when molecules that do not mix with water coalesce to exclude water

Disulfide Bridges

a strong covasalent bond formed when the sulfur of one cysteine monomer bonds to the sulfur of another cysteine monomer

Quaternary Structure

the particular shape of a complex, aggregate protein, defined by the characteristics three-dimensional arrangement of its constituent subunits, each a polypeptide

Denaturation

in proteins, a process in which a protein unravels and loses its native shape, thereby becoming biologically inactive; in DNA, the seperation of two strands of the double helix

a protein molceule that assist in the proper folding of other proteins

X-Ray Crystallography

a technique that depends on the diffraction of an X-ray beam by the individual atoms of a crystallized molecule tostudy the three-dimensional structure of the molecule

Nucleic Acids

a polymer (polynucleotide) consisting of many nucleotide monomers; serves as a blueprint for proteins and, through the actions of proteins, for all cellular activities

the two types are DNA and RNA

Ribonucleic Acid (RNA)

a type of nucleic acid consisting of nucleotide monomers with a ribose sugar and the nitrogen bases adenine (A), cytosine (C), guanine (G), and uracil (U); usually single-stranded; functions in protein synthesis, gene regulation, and as the genome of some viruses

Polynucleotides

a polymer of consisting of many nucleotide monomers in a chain; nucleotides can be those of DNA or RNA

Nucleotides

the building block of a nucleic acid, consisting of a five-carbon sugar covalently bonded to a nitrogenous base and a phosphate group

Pyrimidine

one of two types of nitrogenous bases found in nucleotides, characterized by a six-membered ring

cytosine (C), thymine (T), and uracil (U) are pyrimidines

Purines

one of two types of nitrogenous bases found in nucleotides, characterized by a six-membered ring fused toa five membered ring

adenine (A), and guanine (G) are purines

Ribose

the sugar component of RNA nucleotides

Deoxyribose

the sugar component of DNA nucleotides, having one fewer hydroxyl group than ribose, the sugar component of RNA nucleotides

Double Helix

the form of native DNA, refering to its two adjavent antiparallel polynucleotide strands wound around an imaginary axis into a spiral shape

Antiparallel

the opposite arrangement of the sugar-phosphate backbones in a DNA double helix

Light Microscope (LM)

an optical instrument with lenses that refract (bend) visible light to magnify images of specimens

Electron Microscope (EM)

a microscope that uses magnets to focus an electron beam on or through a specimen, resulting in resolving power a thousandfold greater than that of a light microscope

a transmission electron microscope (TEM) is used to study the internal structure of thin sections of cells

a scanning electron microscope (SEM) is used to study the fine details of cell surfaces

Cell Fractionation

the disruption of a cell and separation of it sparts by centrifugation

Cytosol

the semifluid portion of the cytoplasm

Nucleoid

a dense region of DNA in a prokaryotic cell

Cytoplasm

the contents of the cell, exclusive of the nucleus and bounded bythe plasma membrane

Plasma Membrane

the membrane at the boundary of every cell that acts as a selective barrier, regulation the cell's chemical composition

Animal Cells

Plant Cells

Nuclear Envelope

the double membrane in a eukaryotic cell that encloses the nucleus, seperating it from the cytoplasm

Nuclear Lamina

a netlike array of protein filaments lining the inner surface of the nuclear envelope; it helps maintain the shape of the nucleus

Chromosomes

a cellular structure carrying genetic material, found in the nucleus of eukaryotic cells

each chromosome consists of one very long DNA molecule and associated proteins

Chromatin

the complex of DNA and proteins that makes up a eukaryotic chromosome

when the cell is not divinding, chromatin exists in its dispersed form, as a mass of very long, thin fibers that are not visible with a light miroscope

Nucleolus

a specialized structure in the nucleus, consisting of chromatin regions containing ribosomal RNA genes along with ribosomal proteins imported from the cytoplasmis site of rRNA sunthesis and ribosomal subunit assembly

Ribosomes

a complex of rRNA and protein molecules that functions as a site of protein synthesis in the cytoplasm; consists of a large and a small subunit

in eurkaryotic cells, each subunit is assebled in the nucleolus

Endomembrane System

the collection of membranes inside and around a eukaryotic cell, related either through direct physical contact or by the transfer of memraneous vesicles; includes the smooth and rough endoplasmic reticulum, the golgi apparatus, lysosomes, and vacuoles

Vesicles

a sac made of membrane in the cytoplasm

Endoplasmic Reticulum (ER)

an extensive membranenous network in eukaryotic cells, continuous with the outer nuclear membrane and composed of ribosome-studded (rough) and ribosome-free (smooth) regions

Smooth ER

that portion of the ER that is free of ribosomes

Rough ER

that portion of the ER studded with ribosomes

Glycoproteins

a protein with one or more carbohydrates covalently attached to it

Transport Vesicles

a tiny membranous sac in a cell's cytoplasm carrying molecules produced by the cell

Golgi Apparatus

an organelle in eukaryotic cells consisting of stacks of flat membranous sacs that modify, store, and route products of the endoplasmic reticulum and synthesize some products, notably noncellulose carbohydrates

Lysosome

a membrane-enclosed sac of hydrolytic enzymes found in the cytoplasm of animal cells and some protists

Phagocytosis

a type of endocytosis in which large particulate substances are taken up by a cell

it is carried out by some protist and by certain immune cells of animals (in mammals, maunly macrophaages, neutrophils, and dendritic cells)

Food Vacuoles

a membranous sac formed by phagocytosis of microorganisms or particles to be used as food by the cell

Contractile Vacuoles

a membranous sac that helps move excess water out of certain freshwater protists

Central Vacuole

a membranous sac in a mature plant cell with diverse roles in reproduction, growth, and development

Mitochondria

an organelle in eukaryotic cells that serves as the site of cellular respiration

Chloroplasts

an organelle found in plants and photosynthetic protist that absorbs sunlight and uses it to drive the synthesis of organic compounds from carbon dioxide and water

Peroxisome

an organelle containing enzymes that transfer hydrogen (H2) from various substrates to oxygen (O2) producing and then degrading hydrogen peroxide (H2O2)

Mitochondrial Matrix

the compartment of the mitochondrion enclosed by the inner membrane and containing enzymes and substrates for the citric acid cycle

Cristae

an infolding of the inner membrane of a mitochondrion that houses electron transport chains and molecules of the enzyme catalyzing the synthesis of ATP (ATP synthase)

Plastids

one of a family closely related organelles that includes chloroplasts, chromoplasts, and amyloplasts (leucoplasts)

plastids are cound in cells of photosynthetic organism

Thylakoids

a flattened membrane sac inside a chloroplast

thylakoids exist in an interconnected system in the chloroplast and contain the molecular "machinery" used to conveert light energy to chemical energy

Granum

a stack of membrane-bounded thylakoids in the chloroplast

grana function in the light reactions of photsynthesis

Stroma

within the chlorooplast, the dense fluid of the chloroplast surrounding the thylakoid membrane; involved in the synthesis of organic molecules from carbon dioxide and water

Cytoskeleton

a network of microtubules, microfilaments, and intermediate filaments that branch throughout the cytoplasm and serve a variety of mechanical, transport, and signaling functions

Motor Proteins

a protein that interacts with cytoskeletal elements and other cell components, producing movement of the whole cell or parts of the cell

Microtubules

a hollow rod composed of tubilin proteins that make up part of the cytoskeleton in all eukaryotic cells and is found in cilia and flagella

Centrosome

structure present in the cytoplasm of animal cells, important during cell division; functions as a microtubule-organizing center:a centrosome has two centrioles

Centrioles

a structure in the centrosome of an animal cell composed of a cylinder of microtubule triplets arranged in a 9 + 0 pattern

a centrosome has a pair of centrioles

Flagella

a long cellular appendage specialized for locomotion

like motile cilia, eukaryotic flagella have a core with nine outer doublet microtubules and two inner ingle micrutubules ensheathed in an extension of the plasma membrane

the basal body may organize the microtubule assembly of a cilium or flagellum and is structurally very similar to a centriole

Dyneins

in cilia and flagella, a large contractile protein esxtending from one mirotubule doublet to the adjacent doublet

ATP hydrolysis drives changes in dynein shape that lead to bending of cilia and flagella

Microfilaments

a cable composed of actin proteins in the cytoplast of almost every eukaryotic cell, making up part of the cytoskeleton and acting alone or wiht myosin to cause cell contraction; also known as actin filament

Actin

a globular protein that links into chains, two of which twist helically about each other, forming microfilaments (actin filaments) in muscle and other kinds of cells

Cortex

(1) the outer region of cytoplasm in a eukaryotic cell, lying just under the plasma membrane, that has a more gel-like consistency than the inner regions, due to the presence of multiple microfilaments

(2) in plants gorund tissue that is between the vascular tissue and dermal tissue in a root or eudicot stem

Myosin

a type of protein filament that acts as a motor protein with actin filaments to cause cell contraction

Pseudopodia

a cellular extension of amoeboid cells used in moving and feeding

Cytoplasmic Streaming

a circular flow of cytoplasm, involving myosin and actin filaments, that speeds the distribution of material within cells

Intermediate Filaments

a component of the cytoskeleton that includes filaments intermediate in size between microtubules and microfilaments

Cell Wall

a protective layer external to the plasma membrane in the cells of plants, prokaryotes, fungi, and some protists

polysaccharides such as cellulose (in plants and some protists), chitin (

in fungi), and peptioglycan (in bacteria) are an important structural component of cell walls

Primary Cell Wall

in plants, a relatively thin and flecible layer first secreted by a young cell

Middle Lamella

in plants, a thin layer of adhesive extracellular material, primarily pectins, found between the primary walls of adjacent young cells

Secondary Cell Wall

in plants, a strong and durable matrix often deposited in several laminated layers for cell protection and support

Extracellular Matrix (ECM)

Collagen

a glycoprotein in the extracellular matrix of animal cells that forms strong fibers, found extensively in connective tissue and bone; the most abundant protein in the animal kingdom

Proteoglycans

a glycoprotein consisting of a small core protien with many carbohydrate chains attached, found in the cellular matrix of animals

a proteoglycans may consists of up to 95% carbohydrate

Fibronectin

a glycoprotein that helps animal cells attach to the extracellular matrix

Integrins

in animal cells, a transmembrane receptor protein that interconnects the extracellular matric and the cytoskeleton

Plasmodesmata

an open channel in the cell wall of a plant through which strands of cytosol connect from an adjacent

Selective Permeability

a property of biological membranes that allows them to regulate the passage of substances

Amphipathic

having both a hydrophilic region and a hydrophobic region

Fluid Mosaic Model

the currently accepted model of cell membrane structure, which envisions the membrane as a mosaic of protein molecule drifting laterally in a fluid bilayer of phospholipids

Integral Proteins

typically a transmembrane protein with hydrophobic regions that extend into and often completely span the hydrophobic interior of the membrane and with hydrophilic regions in contact with the aqeuous solution on either sife of the membrane (or lining the channel in case of a channel protein)

Glycolipids

a lipid with a covalently attached carbohydrate

Glycoproteins

a protein with one or more carbohydrates covalently attached to it

Transport Proteins

a transmebrane protein that helps a certain substance or class of closely related substance to cross the membrane

Aquaporins

a channel protein in the plasma membrane of a plant, animal, or microorganism cell that specifically facilitates osmosis, the diffusion of water across the membrane

Diffusion

the spontaneous movement of a substnace downits concentration gradient, from a region where it is more concentrated to a region where it is less concentrated

Concentration Gradient

a region along which the density of a chemical substance increases or decreases

Passive Transport

the diffusion of a substance accross a biological membrane with no expenditure of energy

Osmosis

the diffusion of water across a selectively permeable membrane

Tonicity

the ability of a solution surrounding ca cell to cause that cell to gain or lose water

Isotonic

referring to a solution that, when surrounding a cell, has no effect on the passage of water into or out of the cell

Hypertonic

referring to a solution that, when surrounding a cell, will cause the cell to lose water

Hypotonic

referring to a solution that, when surrounding a cell, will cause the cell to take up water

Osmoreregulation

regulation of sultoe concentrations and water balane by a cell or organism

Flaccid

limp. lacking in stiffness or firmness, as in a plant cell in surroundings where there is no tendency for water to enter the cell

Plasmolysis

a phenomenon in walled cells in which the cytoplasm shrivels and the plasma membrane pulls away from the cell wall; occurs when the cell loses water to a hypertonic environment

Facilitated Diffusion

the spontaneous passage of molecules or ions across a biological membrane with the assistance of specific transmembrane transport proteins

Ion Channels

a transmembrane protein channel that allows a specific ion to flow across the mrembrane down its concentration gradiet

Gated Channels

a transmembrane protein channel that opens or closes in response to a particular stimulus

Active Transport

the movement of a substance across a cell membrane, wiht an expenditure of energy, against its concentration or electrochemical gradient; mediated by specific transport proteins

Sodium-Potassium Pump

a transport protein in the plasma membrane of animal cells that actively transports sodium out of the cell and potassium into the cell

Membrane Potential

the difference in electrical charge (voltage) across a cell's plasma membrane, due to the differential distribution of ions

membrane potential affects the activity of excitable cells and the transmembrane movement of all charge substances

Electrochemical Gradient

the diffusion gradient of an ion, whwich is affected by both the concetration difference of the ion across a membrane (a chemical force) and the ion's tendency to move relative to the membrane potential 9 an electron force)

Electrogenic Pump

an ion transport protein that generates volage across a membrane

Proton Pump

an active transport protein in cell membrane that uses ATP to transport hydrogen ions out of a cell against their concentration gradient, generating a membrane potential in the process

Cotransport

the coupling of the "downhill" diffusion of one substance to the "uphill" transport of another against its own concentration gradient

Exocytosis

the cellular secretion of biological molecules by the fusion of vesicle containing them with the plasma membrane

a type of endocytosis in which large particulate substances are taken up by a cell

it is carried out by some protists and by certain immune cells of animals (in mammals, mainly macrophages, neutrophils, and dendritic cells)

Receptor-Mediated Endocytosis

the movement of specific molecules into a cell by th einward budding of memebranous vesicles containing proteins with receptor sites specific to the molecules being taken in;enables a cell to aquire bulk quanities of specific sunstance

Pinocytosis

a type of endocytosis in qhich the cell ingests extracellular fluids and its dissolved solutes

Ligands

a molecule that binds specificaly to another molecule, usually a larger one

Metabolism

the totality of an organism's chemical reactions, consisting of catabolic and anabolic pathways, which ,manage the material and energy resources of the organism

Metabolic Pathway

a series of chemical reactions that either builds a complex molecule (anabolic pathway) or breaks down a complex molecule into simpler compounds (Catabolic pathway)

Catabolic Pathways

a metabolic pathway that releases energy by breaking down complex molecules to simpler compounds

Anabolic Pathways

a metabolic pathway that consumes energy to sunthesize a complex molecule from simpler compounds

Bioenergetics

(1) the overall flow and transformation of energy in an organism

(2) the study of how energy flows through organisms

Energy

the capacity to cause change, especially to do work (to move matter against an opposing force)

Kinetic Energy

the energy associated with relative motion of objects

moving matter can perform work by imparting motion to other matter

Heat

the total amount of kinetic energy due to the random motion of atoms or molecules in a body of matterl also called thermalenergy

heat is energy in its most random form

Potential Energy

the energy that matter posesses as a result of its location or spatial arrangement (structure)

Chemical Energy

energy available in molecules for release in a chemical reaction; a form of potential energy

Thermodynamics

the study of energy transformation that occur in a collection of matter

First Law of Thermodynamics

the principle of conservation of energy: energy can be transferred and transformed, but it cannot be created or destroyed

Entropy

a measure of disorder, or randomness

Second Law of Thermodynamics

the principle stating that eevery energy transfer or transformation increases the entropy of the universe

ordered forms of energy are atleast partly converted to heat

Free Energy

the portion of a biological system's energy that can perform work when temperature and pressure are uniform throughout the system (delta G)

Exergonic Reaction

a spontatneous chemical reaction, in which there is a net realeaseof free energy

Endergonic Reaction

a nonspontaneous chemical reaction, in which free energy is absorbed from the surroundings

Energy Coupling

in cellular metabolism, the use of energy released from an exergonic reaction to drive an endergonic reaction

ATP (Adenosine Triphosphate)

an adenine-containing nucleosidic triphosphate that releases free energy when its phosphate bonds are hydrolyzed

this energy is used to drive endergonic reactions in cells

Phosphorylated

referring to a molecule that is covalently bonded to a phosphate group

Enzyme

a macromolecule serving as a catalyst, a chemical agent that changes the rate of a reaction wihtout being consumed by the reaction

Catalyst

a chemical agent that increases the rate of a reaction without being consumed by the reaction

Activation Energy

the amount of energy that reactants must abosorb before a chemical reaction will start; also called free energy of activation

Substrate

the reactant of which an enzyme works

Enzyme-Substrate Complex

a temporar complex formed when an enzyme binds to its substate molecules

Active Site

the specificportion of an enzyme that binds th substrate by means od multiple weak interactionsand that forms the pocket in which catalysis occurs

Induced Fit

induced by entry of substrate, the change in shape of the active site of an enzyme so that it binds more snugly to the substrate

Cofactors

any nonprotein molecule or ion that is required for the proper functioning of an enzyme

cofactors can be permanently bound to the active site or may bind loosely with the substrate during catalysis

Coenzyme

an organic molecule serving as a cofactor

most vitamins function as coenzymes in metabolic reactions

Competitive Inhibitors

a substance that reduces the activity of an enzyme by enetering the active site in place of the substrate whose structure it mimics

Noncompetitive Inhibitors

Allosteric Regulation

the binding of a regulatory molecule to a protein at one site that affects the functions of the protein at a different site

Cooperativity

a kind of allosteric regulation whereby a shape change in one subunit of a protein caused by substrate binding is transmitted to all the others, facilitating binding of subsequent substrate molecules

Feedback Inhibition

a method of metabolic control in which the end product of a metbolic pathways acts as an inhibitor of an enzyme within that pathway

Fermentation

a catabolic process that makes a limited amount of ATP from glucose without an electron transport chain and that produces a characteristic end product, such at ethyl alcohol or lactic acid

this is the most efficient catabolic pathway and is carried out in most eukaryotic cells and many prokaryotic organisms

Cellular Respiration

the catabolic pathways of aerobic and anaerobic respiration, which break down organic molecules for the production of ATP

Redox Reactions

a chemical reaction involving the complete or partial transfer of one or more elctrons from one reactant to another; short for oxidation-reduction reaction

Oxidation

the loss of electrons from a substance involved in a redox reaction

Reduction

the addition of electrons to a substance involved in a redox reaction

Reducing Agent

the electron donor in a redox reaction

Oxidizing Agent

the electron acceptor in a redox reaction

NAD

nicotinamide adenine dinucleotide, a coenzyme that cann accept an electron and acts as an electron carrier in the elctron transport chain

Electron Transport Chain

a sequence of electron carrier molecules (

membrane proteins) thazt shuttle electrons during the redox reactions that release energy used to make ATP

Glycolysis

the spitting of glucose into pyruvate

glycolysis occurs in almost all living cells, serving as the starting point for fermentation or cellular respiration

The Citric Acid Cycle

a chemical cycle involving eight steps that completes the metabolic breakdown of glucose molecules begun in gllycolysis by oxidizing pyruvate to carbon dioxide; occurs within the mitochondrion in eukaryotic cells and in the cytosol of prokaryotes; the second major stage in cellular respiration

Oxidative Phosphorylation

the production of ATP using energy derived from the redox reactions of an electron transport chain, the thiird major stage of cellular respiration

Chemiosmosis

an energy-coupling mechanism that uses energy sotrd in the form of a hydrogen ion gradient across a membrane to drive cellular work, such as the synthesis of ATP

most ATP sunthesis in cells occurs by chemiosmosis

Substrate-Level Phosphorylation

the formation of ATP by an enzyme directly transferring a phsophate gorup to ADP from an intermediate substrate in catabolsim

Acetyl CoA

acetyl coenzyme A; the entry compound for the citric acid cycle in cellular respiration, formed from a fragment of pyruvate attached to a coenzyme

Cytochromes

an iron-containing protein that is a component of electron transport chains in the mitochondria and chloroplasts of eukaryotic cells and the plasma membranes of prokaryotic cells

ATP Synthase

a complex of several membrane proteins that drive a port through which protons diffuse

this complex function in chemiosmosis with adjacent electron trsport chains, using the energy of a hyrgen ion ( proton) concentration gradient to make ATP

ATP synthases are found in the inner mitochondrial membrane of eukaryotic cells and in the plasma membrane of prokaryotes

Proton-Motive Force

the potential energy stored in the form of an electrocheical gradient, generated by the pumping of hydrogen ions across a biological membrane during chemiosmosis

Alcohol Fermentation

glycolysis followed by the conversion of pyruvate to carbon dioxide and ethyl alcohol

Lactic Acid Fermentation

glycolysis followed by the conversion of pyruvate to lactate, with no release of carbon dioxide

Obligate Anaerobes

an organism that only carries out fermentation or anaerobi respiration

such organisms cannot use oxygen and in fact may be poisoned by it

Facultative Anaerobes

an organism that makes ATP by aerobic respiration if oxygen is present but that switches to anaerobic respiration or fermentation if oxygen is not present

Beta Oxidation

a metabolic sequence that breaks fatty acids down to two-carbon fragments that enter the citric acid cycle as acetyl CoA

Photosynthesis

the conversion of light energy to chemical energy that is stored in sugars or other organic compounds; occurs in plants, algae, and certain prokaryotes

Autotrophs

an organism that obtains organic food molcules without eating other organisms

autotrophs use energy from the sun or from the oxidation of inorganic substances to make organic molecules from inorganic ones

Chlorphyll

a green pigment located within the chloroplasts of plants and algae and in the membranes of certain prokaryotes

chlorophyll a participates directly in the light reactions, which convert solar energy to chemical energy

Mesophyll

the ground tissue of a leaf, sanwhiched between the upper and lower epidermis and specialized for photosynthesis

Stomata

a microscopic pore surrounded by guard cells in the epidermis of leaves and stems that allows gas exchange between the environment and the interior of the plant

Stroma

within the chloroplast , the dense fluid of the chloroplast surrounding the thylakoid membrane, involved in the synthesis of organic molecules from carboin dioxide and water

Thylakoids

a flattened membranous sac inside a chloroplast

thylakoids exist in an interconnected system in the chloroplast and contain the molecular "machinery" used to convert light energy to chemical energy

Light Reactions

the first of two major stages in photsynthesis (preceding the calvin cycle)

these reactions, which occur on the thylakoid memrbanes of the chloroplast or on membranes of certian prokaryotes, convert solar energy to the chemical energy of ATO and NADPH, releasing oxygen in the process

Calvin Cycle

the second of two major stages in photsynthesis (following the light reactions), involving fixation of atmosphereic CO2 and reduction of the fixed carbon into carbohydrate

the process of generating ATP from ADP and phosphate by means of a proton-motive force generated across the thylakoid membrane of the chloroplast or the membrane of certain prokaryotes during the light reactions of photosynthesis

Carbon Fixation

the intiial incorporation of carbon from CO2 into an organic compound by an autotrophic organism ( a plant, another photosynthetic organism, or a chemoautotrophic prokaryote)

Wavelength

the distance between crests of waves, such as those of the electromagnetic spectrum

Electromagnetic Spectrum

the entire spectrum of electromagnetic radiation ranging in wavelength from oless than a nanometer to more than a kilometer

Visible Light

the light portion of the electromagnetic spectrum that can be detected ad various colors by the human eye, ranging in wavelength from about 380 nm to about 750 nm

Photons

a quantum, or discrete quanity, of light energy that behaves as if it were a particle

Spectrophotometer

an instrument that measures the proportions of light of different wavelengths absorbed and transmitted bya pigment solution

Absorption Spectrum

the range of a pigment's ability to absorb various wavelengths of light; also a graph of such a range

Chlorophyll a

a photsyntehtic pigment that participates directly in the light reactions, which convert solar energy to chemical energy

Action Spectrum

a graph that profiles the relative effectiveness of different wavelengths of radiation in driving a particular process

Chlorophyll b

an accesory photosynthetic pigment that transfers energy to chlorophyll a

Carotenoids

an accessory pigment, either yellow or orange, in the chloroplasts of plants and in some proakaryotes

by absorbing wavelengths of light that chlorophyll cannot, carotenoids broaden the spectrum of colors that can drie photosynthesis

Photosystem

a light-capturing unit located in the thylakoid membrane of the chloroplast or in the membrane of some prokaryotes, consisting of a reaction-center complex surrounded by numerous light-harvesting complexes

there are two types of photosystems, I and II; they absorb light best at different wavelengths

Reaction-Center Complex

a complex of proteins associated with a special apir of chlorphyll a molecules and a primary electron acceptor

located centrally in a photosystem, this complex triggers the light reactions of photsynthesis

excited by light energy, the pair of chlorphylls donates an electron the the primary electron acceptor, which passes an electron to an electron transport chain

Light-Harvesting Complex

a complex of proteins associated with pigment molecules (including chlorophyll a, b, and carotenoids) that captures light and energy trnasfers it to reaction-center pigments in a photosystem

Primary Electron Acceptor

in the thylakoid membrane of a chloroplast or in the membrane of some prokaryotes, a specialized molecule that shares the reaction-center complex with a pair of chlorophyll a molcules and that accepts an electron from them

Photosystem II

one of two light-capturing units in chloroplasts' thylakoid membrane or in the membrane of some prokaryotes; it has two molecules of p680 chlorophyll a at its reaction center

Photosystem I

one of two light-capturing units in a chloroplast's thylakoid membrane of some prokaryotes; it has two molecules of p700 chlorophyll a at its reaction center

Linear Electron Flow

a route of electron flow during the light reactions of photosynthesis that involves both photosystems I and II and produces ATP, NADPH, and O2

the net electron flow is from H20 to NADP+

Cyclic Electron Flow

a route of electron flow during the light reactions of photosynthesis that involves only photosystem I and that produces ATP but ot NADPH or O2

Glyceraldehyde-3-Phospate (G3P)

a three-carbon carbohydrate that is the direct product of the calvin cycle; it is also an intermediate in glycolysis

Carbon Fixation

the initialincorporation of carbon from CO2 into an organic compound by an autotrophic organism (a plant, another photsynthetic organism, or a chemoautomtrophic prokaryote)

Reduction

the addition of electrons to a substance involved in a redox reaction

C3 Plants

a plant that uses the calvin cycle for the initital steps that incorporate CO2 into organic material, forming a three-carbon compound as the first stable intermediate

photrespiration generally occurs on hot, dry, bright days, when stomata close and the oxygen concentration in the leaf exceeds that of carbon dioxide

C4 Plants

a plant in which the calvin cycle is preceded by reaction that incorpoarate CO2 into four-carbon compound, the end product of which supplies CO2 for the calvin cycle

Bundle-Sheath Cells

in C4 plants, a type eof photsynthetic cell arranged into tightly packed sheaths around the veins of a leaf

Mesophyll Cells

in C4 plants, a typpe of loosely arranged photosynthetic cell located between the bundle sheath and the leaf surface

CAM Plants

a plant that uses crassulacean acid metabolism, an adaption for photosynthesis dioxide entering open stomata during the night is converted to organic acids, which release CO2 for the Calvin cycle during the day, when stomata are closed

Cell Division

the reproduction of cells

Cell Cycle

an ordered sequence of events in the ife of a cell. from its origin in the division of a parent cell until its own division of a parent ceoll until its own division into two; the eukaryotic cell cycle is composed of interphase (including G1, S, and G2 subphases) and M phase (including mitosis and cytokinesis)

Genome

the genetic material of an organsim or virus; the complete ocmplement of an organism's or viruses's genes along with its noncoding nucleic acid sequences

Somatic Cells

any cell in a multicellular organism except a sperm or egg

Sister Chromatids

either of two copies of a duplicated chromosome attached to each other by proteins at the centromere and, sometimes, along the arms

while joined, two sister chromatids make up one chromosomes; chromatids are eventually serperated during mitosis or meiosis

Centromere

the specialized region fo the chromosomes where two sister chromatids are most closely attached

Mitosis

a process of nuclear divison in eukaryotic cells conventionally divided into five stages; prophase, prometaphase, metaphase, anaphase, and telophase

mitosis conserves chromosomes equally to each of the daughter nuclei

Cytokinesis

the division of the cytoplasm to form two seperate daughter cells immediately after mitosis, meiosis I, or meiosis II

Meiosis

a modified type of cell division in sexually reproducing organisms consisting of two rounds of cell division but only one round of DNA replication

it results in cells with half the number of chromosome sets as the original cell

Mitotic Phase

the phase of the cell cucle that includes mitosis and cytokinesis

Interphase

the period in a cell cycle when the cell is not dividing

during interphase, cellular metabolic activity is high, chromosomes and organellas are duplication, and cell size may invrease

interphase accounts for 90% of the cell cyle

G1 Phase

the first gap or growth phase, of the cell cycle, consisting of the portion of interphase before DNA synthesis begins

S Phase

the synthesis phase of the cell cycle; the portion of interphase during which DNA is replicated

G2 Phase

the second gap or growth phase, of the cell cycle, consisting of the portion of interphase after DNA synthesis occurs

Prometaphase

the second stage of mitosis, in which discrete chromosomes consisting of identical sister chromatids appear, the nuclear envelope fragments, and the spindle micrtubules attach to the kinetochores of the chromosomes

Metaphase

the thrid stage of mitosis, in which the spindle is complete and the chromosomes, attached to mictrubules at their kinectochores, are all aligned at the metaphase

Anaphase

the fourth stage of mitosis, in which the chromatids of each chromosome have sperated and the daughter chromosomes are moving to the poleds of the cell

Prophase

the first stage of mitosis, in which the chromatin condenses, the mitotic spindle begins to form, and the nucleolus disappears, but the nucleus remains intact

Telophase

the fifth and final stage of mitosis, in which daughter nuclei are forming and cytokenesis has typically begun

Mitotic Spindle

an assemblage of microtubules and associated proteins that is involved in the movements of chromosomes during mitosis

Centrosome

structure present in the cytoplasm of animal cells, important durin cell division; functions as a microtubule-organizing center

a centrosome has two centrioles

Aster

a radial array of short microtubules that extendss from each centrosome toward the plasma membrane in an animal cell undergoing mitosis

Kinectochore

a structure of proteins attached to the centromere that links each sister chromatid to the mitotic spindle

Metaphase Plate

an imaginary plane midway between the two poles of a cell in metaphase on which the centromers of all the duplicated chromosomes are located

Cleavage

(1) the process of cytokensis in animall cells, characterized by pinching of the plasma membrane

(2) the succession of rapid cell divisions without significant growth during early embryonic development that converts the zygote to a ball of cells

Cleavage Furrow

the first sign of cleavage in an animall cell; a shallow groove in the cell surface near the old metaphase plate

Cell Plate

a double membrane across the midline of a dividing plant cell, between which the new cell wall forms during cytokinesis

Binary Fusion

a method of asexual reproduction by "division in half"

in prokaryotes, binary fission does not involve mitosis; but in single-celled eukaryotes that undergo binary fission, mitosis is part of the process

Cell Cycle Control System

a cyclically operating set of molecules in the eukaryotic cell that both triggers and coordinates key events in the cell cycle

Checkpoint

a control point in the cell cycle where stop and go-ahead signals can regulate the cycle

G0 Phase

a nondividing state occupied by cells that have left the cell cycle

Cyclin

a cellular protein that occurs in a cyclically fluctuating concentration and that plays an important role in regulating the cell cycle

Cyclin-Dependent Kinases (Cdks)

MPF

maturation-promoting factor (M-phase promoting factor); a protein complex required for a cell to progress from late interphase to mitosis

the active form consists of cyclin and a protein kinase

Growth Factor

(1) a protein must be present in the extracellular environment (culture medium or animal body) for the growth and normal deveoplment of certain types of cells

(2) a local regulator that acts on nearby cells to stimulate cell proliferation and differientation

Density-Dependent Inhibition

the phenomenon observed in normal animal cells that causes them to stop dividing when they come into contact wiht one another

Anchorage Dependence

the requirement that a cell must be attached to a substratum in order to divide

Benign Tumor

a mass of abnormal cells that remains at the site of its origin

Malignant Tumor

a cancerous tumr that is incasice enough to impair the functions of one or more organs

Metastasis

the spread of cancer cells to locations distant from their original site

Heredity

the transmission of traits from one generation to the next

Variation

differences between members of the same species

Genetics

the scientific study of hereditary and hereditary variation

Genes

a discrete unit of hereditary information consisting of a specific nucleotide sequence in DNA (or RNA, in some viruses)

Gametes

a haploid reproductive cell suchas an egg or sperm

gametes unite during sexual reproduction to produce a diploid zygote

Asexual Reproduction

the generation of offspring froma single parent that occurs without the fusion of gametes (by budding, division of a single cell, or division of the organism into two or more parts) in most cases, the offspring are genetically identical to the parent

Clone

(1) a lineage of genetically identical individuals or cells

(2) in popular usage, a single individual organism that is genetically identical to another individual

(3) as a verb, to make one or more genetic replicas of an individual or cell

Sexual Reproduction

a type of reproduction in which two parents give rise to offspring that have unique combinations of genes inherited from the gametes of the parents

Life Cycle

the generation-to-generation seqeunce of stages in the reproductive history of an organism

Karyotype

a display of the chromosome pairs of a cell arranged by size and shape

Homologous Chromosomes

a pair of chromosomes of the same lenth, centriomer position, and staining pattern that possess genes for the same characters at corresponding loci

one homologous chromosome is inherited from the organism's father, the other from the mother

also called homologs, or homologous pair

Sex Chromosomes

a chromosome responsible for determining the sex of an individual

Autosomes

a chromosome that is not dierectly involved in determining sex; not a sex chromosomes

Diploid Cell

a cell containing two sets of chromosomes (2n), one set inhherited from each parent

Haploid Cells

a cell containing only one set of chromosomes (n)

Ferilization

(1) the union of haploid gametes to pruduce a diploid zygote

(2) the addition of mineral nutrients to the soil

Zygote

the diploid product of the union of haploid gametes during fertilization; a fertilized egg

Alternation of Generations

a life cycle in which there is both a multicellular diploud form, the sporophyte, and a multicellular haploid form, the gametophyte; characteristic of plants and some algae

Sporophyte

in organisms (plants and some algae) that have alternation of generations, the multicellular diploid form that results from the union of gametes

the sporophyte produces haploid spores by meiosis that develop into gametophytes

Spores

(1) in the life cycle of a plant or alga undergoing alternation of generations, a haploid cell produced in the sporophyte by meiosis

a spore can be divided by mitosis to develop into a multicellular hapoliod individual, the gametphyte, without fusing with another cell

(2) in fungi, a haploid cell, produced either sexually or asexually, that produces a myceliu, after germination

Gametophyte

in organisms (plants and some algae) that have alternation of generations, the multicellular haploid form that produces haploid gamets bhy mitosis

the haploid gametes unit and develop into sporophytes

Meiosis I

the first division of a two stage process of cell division in sexually repoducing organisms that results in cells with half the number of chromosome sets as the original cell

Meiosis II

the second division of a two stage process of cell division ins exually reproducing organisms that results in cells with half the number of chromosome sets as the original cell

Synapsis

the pairing and replication of homologous chromosomes during prophase 1 of meiosis

Crossing Over

the reciprocal exchange of genetic material between nonsister chromatids during prophase I of meiosis

Chiasma

the x-shaped, microscopically visible region where homologous nonsister chromatids have exchanged genetic material through crossing over during meiosis, the two homologs remaining associated due to sister chromatid cohesion

Recombinant Chromosomes

a chromosome created when crossing over combines the DNA from two parents into a single chromosome

True-Breeding

referring to plants that produces offspring of the same variety when they self-polinate

Hybridization

in genetics, the mating, or crossing, of two true-breeding varieties

P Generation

the parent individuals fromw hich offspring are derived in studies of inheritance, p stands for parental

F1 Generation

the first filial, or hybrid, offspring in a series of genetic crosses

F2 Generation

offspring resulting from interbreeding of the hybrid F1 generation

Alleles

any of the alternative versions of a gene that produce distingushable phenotypic effects

Dominant Allele

an allele that is fully expressed in the phenotype of a heterozygote

Recessive Allele

an allele whose phenotypic effect is not observed in a heterozygote

Law of Segregation

Mendel's first law, stating that the two alleles in a pair segregate (seperate) into different gametes during gamete formation

Punnett Square

a diagram used in the study of inheritance to show the predicted resolts of random fertilization in genetic crosses

Homozygous

having two identical alleles for a given gene

Heterozygous

having two different alleles for a given gene

Phenotype

the physical and physiolgoical traits of an organism, which are determined by its genetic makeup

Genotype

the genetic make up, or set of alleles, of an organism

Testcross

breeding on organism of unkown genotype with a homozygous recessive individual to determine the unkown genotype

the ratio of phenotypes in the offspring reveals the unknown genotype

Monohybrids

an organism that is heterozygous with respect to a single fene of interest

all the offspring from a cross between parents homozygous for different alleles are monohybrids

for example, parents of genotypes AA and aa produce a monohybrid of genotype Aa

Dihybrids

an organism that is heterozygous with respect to two genes of interest

all the offspring from a cross between parents doubly homozygous for different alleles are dihybrids

for example, parents of genotypes AABB and aabb produce a dihybrid of genotypes AaBb

Law of Independent Assortment

Mendel's second law, stating that each pair of alleles segregates, or assorts, indepependently of each other pair during gamete formationl applies when genes for two characters are located on different pairs of homologous chromosomes

Complete Dominance

the situation in which phenotypes of the heterozygote and dominant homozygote are indistinguishable

Incomplete Dominance

the situation in which the phenotype of heterozygous is intermediate between the phenotypes of individuals homozygous for either allele

Codominance

the situation in which the pheotypes of both allels are exhibited in the heterozygote because both allels affect the phenotype in seperate, distinguishable ways

Tay-Sachs Disease

a human genetic disease caused by a recessive allele for a dysfunctional enzyme, leading to accumalition of certain lipids in the brain, seizures, blindness, and degeneration of motor and mental performance usually become manifest a few months after birth, followed by death within a few years

Pleiotropy

the ability of a single gene to have multiple effects

Epistasis

a type of gene interaction in which one gene alters the phenotypic effects of another gene that is independently inherited

Quantitative Characters

a heritable feature that varies continusously over a range rathen than in an either-or fashion

Polygenic Inheritance

an additive effect of two or more genes on a single phenotypic character

Norm of Reaction

the range of phenotypes produced by a single genotype, due to environmental influences

Multifactorial

referring to a phenotypic character that is influenced by multiple genes and environmental factors

Pedigree

a diagram of a family tree showing the occurrence of heritable characters in parents and offspring over multiple generations

Cystic Fibrosis

a human genetic disorder caused by a recessive allele for a chloride channel protein; characterized by an ecessive secretion of mucus and consequent vulnerabilty to infection; fatal if untreatedd

Sickle-Cell Disease

a human genetic disease by a recessive allele that results in the substitution of a single amino acid in a globin polypeptide that is part of the homoglobin protein; characterized by deformed red blood cells (due to protein aggregation) that can lead to numerous symptoms

Huntington's Disease

a human genetic disease caused bya dominant allele, characterized by uncontrollable body movements and degeneration of the nervous systemm; usually fatal 10 to 20 years after onset of symptoms

Amniocentesis

a technique of prenatal diagnosis in which amniotic fluid, obtained by aspiration from a needle inserted into the uterus, is analyzed to detect certain genetic and congenital defects in the fetus

Chorionic Villus Sampling (CVS)

a technique of prenatal diagnosis in which a small sample of the fetal portion of the placenta is removed and analyzed to detect certain genetic and congenital defects in the fetus

Transformation

(1) the conversion of a normal animal cell to a cancerous cell

(2) a change in genotype and phenotype due to the assimilation of external DNA bya cell

Bacteriophages

a virus that infects bacteria; also called a phage

Phages

a virus that infects bacterial also called bateriophage

Double Helix

the form of native DNA, refering to its two adjacent antiparallel polynucleotide strands wound around an imaginary axis into a spiral shape

Semiconserative Model

the type of DNA replication in which the replicated double helix consists of one old strand, derived from the old molecule, and one newly made strand

Origins of Replication

site where the replication of a DNA molecule begins, consisting of a specific sequnece of nucleotides

Replication Fork

a y-shaped region on a replicating molecule where the parental strands are being unwound and new strands are growing

Helicases

an enzyme that untwists the double helix of DNA at the replication forks, seperating the two strands and making them available as tmeplate strands

Single-Strand Binding Proteins

a protein that binds to the unpaired DNA strands during DNA replication, them and holding them apart while they serve as template for the synthesis of complementary strands of DNA

Topoisomerase

a prtotein that breaks, swivels, and rejoins DNA strands

during DNA repliation, topoisomerase helps to relieve strain in the double heliz ahead of the replication fork

Primase

an enzyme that joins RNA nucleotides to make the primer using the parental DNA strand as a template

Primer

a short stretch of RNA with a free 3' end, bound by complementary base pairing to the template strand, that is elongated with DNA nucleotides during DNA replication

DNA Polymerases

an enzyme that catalyzes the elongation of new DNA (for example, at a replication fork) by the addition of nucleotides to the 3' end of an existing chain

there are several different DNA polymerases; DNA polymerase III and DNA polymerase I play major roles in DNA replication in prokaryotes

Leading Strand

the new complimentary DNA strand synthesized continously along the template strand toward the replication fork in the madatory 5' to 3' direction

Lagging Strand

a discontinusously synthesized DNA strand that elongates by means of okazaki fragments, each synthesized in 5' to 3'direction away from the replication fork

Okazaki Fragments

a short segment of DNA synthesized away from the replication fork on a template strand during DNA replication, many of which are joined together to make up the lagging strand of newly synthesized DNA

DNA Ligase

a linking enzyme essential for DNA replication; catalyzes the covalent bonding of 3' end of one DNA frazgment (such as Okazaki fragment) to the 5' end of another DNA fragment (such as a growing DNA chain)

an enzyme that cuts DNA or RNA, either removing one or few bases or hydrolyzing the DNA or RNA completely into its component nucleotides

Nucleotide Excision Repair

a repair system that removes and then correctly replaces a damaged segment of DNA using the undamaged strand as a guide

Telomers

the tandemly repeptitive DNA at the end of a eukaryotic chromosome's DNA

molecule that protects the organism's genes from being eroded during successive rounds of replication

Telomerase

an enzyme that catlyzes the lengthening of telomers in eukaryotic germ cells

Nucleiod

a dense region of DNA in a prokaryotic cell

Heterochromatin

eukaryotic chromatin that remains highly compacted during interphase and is generally not transcribed

Euchromatin

the less condensed form of eukaryotic chromatin that is available for transcription

Gene Expression

the process by which the synthesis of proteins or, in some cases, just RNAs

Transcription

teh synthesis of RNA using a DNA template

Messenger RNA (mRNA)

a type of RNA, synthesized using a DNA template, that attaches to ribosomes in the cytoplasm and specifies the primary structure of a protein

Translation

the synthesis of a polypeptide using the genetic information encoded in an mRNA molecule

there is a change of "language" from nucleotides to aminoa cids

Primary Transcript

an initial RNA transcript; also called pre-mRNA when transcribed froma protein-coding gene

Triplet Code

a set of three-nucleotide-long words that specify the amino acids for polypeptide chainse

Template Strand

the DNA strand that provides the pattern, or template for odering the sequence of nucleotides in an RNA transcript

Codons

a three-nucleotide sequence of DNA or mRNA that specifies a particular amino acid or termination signal; the basic unit of the genetic code

Reading Frame

ona mRNA, the triplet grouping of ribonucleotides used by the translation machinery during polypeptide synthesis

RNA Polymerase

an enzyme that links ribonucleotides into a growing chain during transcription

Promotor

a specific nucleotide sequence in DNA that binds RNA polymerase, positioning to start transcribing RNA at the appropriate place

Terminator

in bacteria, a sequence of nucleotides in DNA that marks the end of gene and signals RNA polymerase to release the newly made RNA molecule and detach from the DNA

Transcription Unit

a region of DN A that is transcribed into an RNA molecule

Transcription Factors

a regulatory protein that binds to DNA and affects the transcription of specific genes

Transcription Initiation Complex

the completed assembly of transcription factors and RNA polymerase bound to a promoter

TATA Box

a DNA sequence in eukaryotic promoters crucial in forming the transcription initiation complex

Poly-A Tail

a sequence of 50 to 250 adenine nucleotides added onto the 3' end of a pre mRNA molecule

RNA Splicing

after synthesis of a eukaryotic primary RNA transcript, the removal of portions (introns) of the transcript that will not be included in the mRNA

Introns

a noncoding,intervening sequence within a primary transcript that is removed from the transcript during RNA processing; also refers to the region of DNA from which this sequence was transcribed

Exons

a sequence within a primary transcript which remans in the RNA after RNA processing; also refers to region of DNA from which this sequence was transcribed

Spliceosome

a large complex made up of proteins and RNA molceules that splices RNA by interacting with the ends of an RNA intron, releasing the intron and joining the two adjacent exons

Ribozymes

an RNA molecule that functions as an enzyme, catalyzing reactions during RNA splicing

Alternative RNA Splicing

a type of eukaryotic gene regulation at the RNA-processing level in which different mRNA molecules are produced from the same primary transcript, depending on which RNA segments are treated as exons and which as introns

Domains

(1)a taxonomic category above the kingdom level

the three domains are archaea, bacteria, and eukarya

(2) an independently folding part of a protein

Transfer RNA (tRNA)

an RNA molecule that dunctions as an interpreter between nucleic acid and protein language by picking up specific amino acids and recognizing the appropriate codons in the mRNA

Anticodon

a nucleotide triplet at one end of a tRNA molecule that recognizes a particular complementary codon on an mRNA molecule

Aminoacyl-tRNA Synthetases

an enzyme that joins each amino acid to the appropriate tRNA

Wobble

flexibility in base pairing rules in which the nucleotide at the 5' end of a tRNA anitcodon can form hydrogen bonds with more than one kind of base in the third position (3'end) of a codon

Ribosomal RNAs rRNAs

the most abundant type of RNA, which together with proteins makes up ribosomes

P Site

one of ribosome's three binding sites for tRNA during translatin

the p site holds the tRNA carrying the groqing polypeptide chain

A Site

one of the ribosome's three binding sites for tRNA during translation

the a site holds the tRNA carrying the next amino acid to be added to the polypeptide chain (A stands foe aminoacyl tRNA)

E Site

one of ribosmal's htree bidning sites for tRNA durinf translation

the E site is the place where discharged tRNAs leave the ribosome

Polyribosomes (Polysomes)

a group of several ribosomes attached to, and translating, the same messenger RNA molecule

Signal Peptide

a sequence of about 20 amino acids at or near the leading (amino) end of a polypeptide that targets it to the endoplasmic reticulum or other organelles in a eukaryotic cell

Signal-Recognition Particle (SRP)

a protein RNA-complex that recognizes a signal peptide as it emerges from a ribosome and helps direct the ribosome to en ER by binding to a receptor protein on the ER

Mutations

a change in the nucleotide sequence of an organism's DNA, ultimately creating genetic diversity

mutations also can occur in the DNA or RNA of a virus

Point Mutations

a change in a gene at a single nucleotide pair

Base-Pair Substitution

a type of point mutation; the replacement of one nucleotide and its partner in the complementary DNA strand by another pair of nucleotides

Missense Mutations

a base-pair substitution that results in a codon that codes for a different amino acid

Insertions

a mutation involving the addition of one or more nucleotide pairs ot a gene

Deletions

(1) deficiency in a chromosome resulting from the loss of a fragment through breakage

(2) a mutational loss of one or more nucleotide pairs from a gene

Frameshift Mutation

a mutation occuring when the number of nucleotides inserted or deleted is not a multiple of three, resulting in the improper grouping of the subsequent nucleotides into codons

Mutagens

a chemical or physical agent that interacts with DNA and causes a mutation